Coating composition for a food or beverage can

ABSTRACT

A two component coating composition, suitable for coating onto a metal substrate, especially food and beverage cans, the coating composition comprising:
         a first component comprising an acrylic latex material; and   a second component comprising a functional silane material.

The present invention relates to a coating composition. In particular,the present invention relates to a two component coating compositionsuitable for deposition onto a metal substrate. In one embodiment, thepresent invention relates to a coating composition for repairing a scoreline on a coated metal substrate and to a method of repairing the scoreline incorporating the use of the coating composition.

Metal containers are being equipped more and more with so-called easyopen ends in which a user accesses the interior of the container bypiercing the container in a predetermined manner, without the need for aseparate opening device. Such easy open ends are routinely used in foodand beverage cans.

The principle of easy opening is obtained by reducing the thickness ofthe metal to thereby provide a score line which is weaker andsusceptible to opening. During the scoring operation, which is oftenachieved by stamping with a punch, the external varnish layer is cut andtherefore the corrosion resistance of the metal substrate iscompromised. This is particularly problematic in a context where:

-   -   i) the metal has been stressed and therefore its resistance to        corrosion is weakened    -   ii) the tin layer of the tinplate (where this is the substrate)        is also cut; and/or    -   iii) the next treatment step of the packaging is sterilisation,        where the presence of heat and high humidity will create high        corrosion conditions    -   iv) The container is at the beginning of its life cycle which        has a minimum of two years.

The corrosion resistance of the metal substrate is restored by theapplication of a repair coating to the score line. This coating is oftenapplied by spraying and in particular an airless spray process.

Current repair formulations are generally based on a cross-linkage of anepoxy resin, usually of low molecular weight, by poly(amido amine)s.These compositions are characterised by high volatile organic compounds(VOC), a low cross-linkage speed and a limited pot life (from a fewhours to a week). Furthermore, since these compositions are based onepoxy chemistry, they often contain Bisphenol A(4,4′-(propane-2,2-diyl)diphenol, also known as BPA) or derivativesthereof.

Therefore, present compositions may have drawbacks. In particular, it isdesired to provide such coatings that have a reduced amount of BPA orderivatives thereof.

Also it is desired to provide coatings with reduced levels of volatileorganic content (VOC) when compared to the current compositions.

It is an object of embodiments of the present invention to provide asolution to the above mentioned or other problems.

According to a first aspect of the present invention there is provided atwo component coating composition suitable for coating onto a metalsubstrate, the coating composition comprising:

-   -   a first component comprising an acrylic latex material; and    -   a second component comprising a functional silane material.

Suitably, the acrylic latex material comprises an aqueous emulsion ofone or more acrylic polymers.

Suitably, the acrylic latex material is formed from a reaction mixture,the reaction mixture may comprise one or more C₁ to C₆ alkyl(meth)acrylate material, suitably more than one C₁ to C₆ alkyl(meth)acrylate material. Examples of suitable C₁ to C₆ alkyl(meth)acrylate materials include methyl acrylate; methyl (meth)acrylate;ethyl acrylate; ethyl (meth)acrylate; propyl acrylate; propyl(meth)acrylate; butyl acrylate; butyl (meth)acrylate. The C₁ to C₆ alkyl(meth)acrylate may comprise one or more functional group, such as anepoxy group. For example the C₁ to C₆ alkyl (meth)acrylate may compriseglycidyl methacrylate.

The acrylic polymer(s) each suitably comprise a homopolymer or copolymerof at least one C₁ to C₆ alkyl (meth)acrylate monomer.

Unless stated otherwise, it should be understood that reference hereinto (meth)acrylate indicates that the (meth) group is optional.

Suitably, the reaction mixture further comprises an αβ ethylenicallyunsaturated carboxylic acid or anhydride, Particularly suitable αβethylenically unsaturated carboxylic acid or anhydride are acrylic acidor methacrylic acid.

The reaction mixture may further comprise one or more ethylenicallyunsaturated monomer(s). In one embodiment, the reaction mixture maycomprise an aryl substituted ethylenically unsaturated monomer, such asstyrene, for example.

In one embodiment, the acrylic latex material comprises an aqueousdispersion of an acrylic material in a core/shell arrangement.

The shell may be formed from a plurality of components, which may bereferred to as a shell mixture. The shell mixture suitably comprises oneor more αβ ethylenically unsaturated carboxylic acid such as methacrylicacid, for example. The shell mixture may further comprise one or more C₁to C₆ alkyl (meth)acrylate, such as methyl acrylate, ethyl acrylate orbutyl acrylate, a particularly suitable C₁ to C₆ alkyl (meth)acrylate isethyl acrylate. The shell mixture may further comprise one or moreethylenically unsaturated monomer, such as an aryl substitutedethylenically unsaturated monomer, such as styrene, for example.

The shell mixture may further comprise one or more free radicalinitiators, particularly initiators which are soluble in the monomermixture, such as a peroxy or peroxyester functional substances. Typicalexamples of suitable free radical initiators of this type include,tertiary butyl perbenzoate, tert butyl peroxy 3,5,5 trimethylhexanoate,tertiary butyl peroxy 2-ethyl hexanoate, di tertiary butyl peroxide andtertiary butyl per acetate. Other suitable initiator materials includeazo type initiators, typical examples are 2,2′-azobis(isobutyronitrile),2,2′-Azobis(2-methylbutyronitrile), 2,2′-Azobis(2.4-dimethylvaleronitrile) and 2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile).

Suitably, the shell mixture is caused to undergo polymerisation to forma shell polymer. The polymerisation of the shell mixture is typicallycarried out as a free radical initiated solution polymerisation in asolvent or mixture of solvents. The solvents which may be used in thisprocess include one or more of the following: alcohols such asn-butanol, pentanol or hexanol; or glycol ethers such as 2-butoxyethanol, 1-methoxy propan-2-ol or dipropylene glycol mono methyl ether.

Polymerisation may be carried out at an elevated temperature. Typicallythe polymerisation may be carried out in the range 80° C. to 150° C. Thepolymerisation can be effectively carried out by adding the shellmixture, over a set time period, to the solvent mixture. In oneembodiment, the shell mixture may be caused to undergo polymerisation toform a shell polymer prior to contact with components of the coremixture.

Where the shell mixture comprises one or more αβ ethylenicallyunsaturated carboxylic acid, the shell polymer will have pendantcarboxylic acid functional groups. This may be referred to a carboxylicacid functional shell polymer.

The carboxylic acid functional shell polymer may be contacted with abase to form a water dispersible salt. The carboxylic acid functionalityin the carboxylic acid functional shell polymer may be at least partlyneutralised with the base. Typically at least 10 of the availablecarboxylic acid groups are neutralised. In one embodiment, substantiallyall of the available carboxylic acid groups are neutralised by the base.Suitably, the base used for this neutralisation comprises an aminefunctional material, or a mixture of amine functional materials.Examples of suitable amine functional materials include ammonia,triethylamine, diethylamine, trimethylamine and morphline or hydroxyamine materials such as ethanol amine, N-methyl ethanol amine and N,N dimethyl ethanolamine.

The shell polymer may be dispersed in aqueous medium. Suitably, theshell polymer may be dispersed in aqueous medium. In this manner, anaqueous dispersion or solution of the shell polymer may be formed.

In another embodiment, the shell mixture is caused to undergopolymerisation to form a shell polymer by dispersion polymerisation inan aqueous medium, thereby forming an aqueous dispersion or solution ofthe shell polymer.

The core may be formed from plurality of components, which may bereferred to as a core mixture. Suitably, the core mixture comprises oneor more C₁ to C₆ alkyl (meth)acrylate, such as one or more of methylacrylate, ethyl acrylate or butyl acrylate, a particularly suitable C₁to C₆ alkyl (meth)acrylate is ethyl acrylate. The core mixture mayfurther comprise a functional C₁ to C₆ alkyl (meth)acrylate. Forexample, the C₁ to C₆ alkyl (meth)acrylate may comprise epoxyfunctionality, such as gylcidylmethacrylate; hydroxy functionality, suchas either of hydroxy ethyl methacrylate or 2 hydroxy ethyl acrylate; oralkyl methylol functionality, such as n-butoxymethyl acrylamide. Thecore mixture may further comprise one or more ethylenically unsaturatedmonomer, such as an aryl substituted ethylenically unsaturated monomer,such as styrene, for example.

The polymer formed from the shell mixture, such as an aqueous dispersionthereof, may serve as a dispersant for a subsequent polymerisation,which may be a polymerisation of an α,β ethylenically unsaturatedmonomer mixture, such as the core mixture.

The core mixture may further comprise one or more free radicalinitiators, particularly suitable are initiators that are generallysoluble in the monomer mixture, such as peroxy or peroxyester functionalsubstances. Typical examples of free radical initiators of this typeinclude, tertiary butyl perbenzoate, tert butyl peroxy 3,5,5trimethylhexanoate, tertiary butyl peroxy 2-ethyl hexanoate, di tertiarybutyl peroxide, and tertiary butyl per acetate. Other suitable oilsoluble initiator materials include azo type initiators, such as:2,2′-azobis(isobutyronitrile), 2,2′-Azobis(2-methylbutyronitrile),2,2′-Azobis(2.4-dimethyl valeronitrile) and2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile). Free radicalinitiators which are water soluble may also be used such as, forexample: azo type initiators such as2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate,2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride and2,2′-Azobis(2-methylpropionamidine)dihydrochloride. Other examples ofsuitable water soluble free radical initiators include materials such ashydrogen peroxide, tert butyl hydroperoxide or mixtures such as hydrogenperoxide and benzoin or the redox initiators such as the mixturetert-butyl hydroperoxide, erythrobic acid and ferrous complexes. Watersoluble persulphate initiators such as ammonium persulphate, sodiumpersulphate or potassium persulphate can be used.

Suitably, the core mixture is caused to undergo polymerisation suitablyat a temperature in the range of between about 30° C. to 99° C.,particularly in the range of between about 50° C. to 95° C. and mostsuitably in the range of between about 80° C. to 90°. Polymerisation ofthe core mixture may occur in the presence of the polymer formed bypolymerisation of the shell mixture to thereby form a core/shellpolymer, typically by dispersion polymerisation. A typicalpolymerisation may be carried out by adding the core mixture, at acontrolled rate over a period of time, to an aqueous dispersion of shellpolymer, During the polymerisation the mixture may be mixed, such as bystirring and the temperature may be held generally constant.

Other methods to polymerise the core mixture include, but are notlimited to, mixing all or part of the core ethylenically unsaturatedsubstances with the aqueous dispersion of shell polymer and then addingthe remaining core components, including free radical initiator, to theresulting mixture over a set period of time. Suitable temperatures forthis type of process are typically in the range 50° C. to 95° C.

For the Core/Shell latex composition the ratio of the core mixture(monomers and initiator) to shell mixture (monomers and initiator) istypically between about 20:80 and 90:10 by weight. Suitably, the ratioof the core mixture to shell mixture is between about 60:40 and 80:20 byweight, particularly suitably the ratio of the core mixture to shellmixture components is between about 70:30 and 75:25.

In another embodiment the latex material comprises an aqueous dispersionof an acrylic material with reactive functional groups and stabilizedwith an emulsifier or surfactant material.

In such an embodiment, the emulsifier may be an anionic, cationic or nonionic type stabilizer. Typical examples of anionic emulsifiers includealkyl sulphates, such as sodium dodecyl sulphate or sodium polyoxyethylene alkyl ether sulphate or aryl sulphonates such as sodiumdodecylbenzene sulphonate. Other examples of anionic emulsifiers includethe sulphosuccinates examples of which include the compounds sodiumdiisobutyl sulpho succinate, sodium dioctyl sulpho succinate and sodiumdi cyclohexyl sulpho succinate. Examples of nonionic emulsifiers includefatty alcohol ethoxylates such as poly ethylene glycol mono lauryl etheror fatty acid ethoxylates such as polyethylene glycol mono stearate orpolyethylene glycol mono laurate or polyether block polymers such aspolyethylene glycol/polypropylene glycol block polymers also known aspluronics, typical commercial products of this type include Tergitol XJ,XH or XD from Dow Chemical. Examples of Cationic emulsifiers includeamine salts such as cetyl trimethyl ammonium chloride or benzyl dodecyldimethyl ammonium bromide. It should also be noted that mixtures ofanionic and cationic emulsifiers would not be desirable.

The acrylic latex material according to the present embodiment may beformed from a reaction mixture, the reaction mixture may comprise one ormore C₁ to C₆ alkyl (meth)acrylate material, suitably more than one C₁to C₆ alkyl (meth)acrylate material. Examples of suitable C₁ to C₆ alkyl(meth)acrylate materials include methyl acrylate; methyl (meth)acrylate;ethyl acrylate; ethyl (meth)acrylate; propyl acrylate; propyl(meth)acrylate; butyl acrylate; butyl (meth)acrylate. The C₁ to C₆ alkyl(meth)acrylate may comprise a functional C₁ to C₆ alkyl (meth)acrylate.For example, the C₁ to C₆ alkyl (meth)acrylate may comprise epoxyfunctionality, such as gylcidylmethacrylate; hydroxy functionality, suchas either of hydroxy ethyl methacrylate or 2 hydroxy ethyl acrylate; oralkyl methylol functionality, such as n-butoxymethyl acrylamide.

In some cases the reaction mixture further comprises an αβ ethylenicallyunsaturated carboxylic acid or anhydride, preferably acrylic acid ormethacrylic acid.

The reaction mixture may further comprise one or more ethylenicallyunsaturated monomer(s). In one embodiment, the reaction mixture maycomprise an aryl substituted ethylenically unsaturated monomer, such asstyrene.

The reaction mixture of α,β-ethylenically unsaturated compounds may bepolymerised to form the acrylic latex using free radical initiators.Free radical initiators which are water soluble are commonly used inemulsifier stabilised Latex compositions as one or more of the freeradical initiators for polymerization. Examples of this type ofinitiator include azo type initiators such as2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate;2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride and2,2′-Azobis(2-methylpropionamidine)dihydrochloride. Other examples ofwater soluble free radical initiators include materials such as hydrogenperoxide or mixtures such as hydrogen peroxide and benzoin or the redoxinitiators such as the mixture tert-butyl hydroperoxide, erythrobic acidand ferrous complexes. Water soluble persulphate initiators such asammonium persulphate, sodium persulphate or potassium persulphate can beused.

In some polymerisations, initiators which are soluble in the monomermixture or so called oil soluble initiators can be used, such as peroxyor peroxyester functional substances. Typical examples of free radicalinitiators of this type include, tertiary butyl perbenzoate, tert butylperoxy 3,5,5 trimethylhexanoate, tertiary butyl peroxy 2-ethylhexanoate, di tertiary butyl peroxide, and tertiary butyl per acetate.Other oil soluble initiator materials include azo type initiators,typical examples are 2,2′-azobis(isobutyronitrile),2,2′-Azobis(2-methylbutyronitrile); 2,2′-Azobis(2.4-dimethylvaleronitrile) and 2,2′-Azobis(4-methoxy-2.4-dimethyl valeronitrile).

Polymerization may be carried out at temperatures in the range ofbetween about 30° C. to 99° C., preferrably in the range 50° C. to 95°C. and most preferably in the range 75° C. to 90° C. The temperature istypically held constant throughout the polymerization process.

The process of forming the emulsifier stabilised latex polymer can beachieved in a number of ways. In all cases the emulsifier is mixed withwater and the mixture heated to the polymerisation temperature, as thefirst part of the process. In some process methods all of the monomercomponents can be mixed with water and emulsifier at the start of theprocess and then, when at temperature, the initiator materials can beadded to the reaction mixture either continuously or in portions over aset time period. An alternative process is for all of the monomermixture and the initiator mixture to be added to the mixture ofemulsifier and water over a set time period at a constant rate. Otheralternative process methods utilise a combination of these techniques,in so much as a part of the monomer mix or initiator (or both) is addedto the emulsifier and water mixture at the start of polymerisation. Theremaining monomer mix and initiator is then added to the reactionmixture over a set time period whilst maintaining a pre determinedtemperature. The appropriate process method which provides a stablelatex material with the desired characteristics, from the chosenreaction components is utilised

The term polymer as used herein refers to a homopolymer or copolymerunless otherwise stated. Furthermore, the term copolymer refers to apolymer formed from two or more different monomers. For example, theterm copolymer as used herein refers to a polymer that may be formedfrom 2, 3, 4, 5 or more different monomers.

The functional silane material comprises one or more functional groups.It is believed that the functional groups allow the coating to adhere tothe metal substrate, although the inventors do not wish to be bound bythis. Such functional groups may include one or more of methoxy, ethoxy,alkoxy, hydroxy, methyldimethoxy, methoxy-ethoxy, methyldimethoxy,ethyltrimethoxy for example.

The functional silane material may be any silane material comprising amolecule having a single or multiple silicon atoms. This includespolysilanes, polysiloxanes or other silicon containing polymers.

In other embodiments, the functional silane material comprisesfunctional groups that react with the acrylic latex material. Suchfunctional groups include aminopropyl, aminoethyl-aminopropyl,phenyl-aminopropyl, benzylamine, phenyl, vinyl, vinyltrichloro,vinylbenzylamine, glycidoxypropyl, methacrylate, isocyanate,3,4-epoxycyclohexyl, methacryloxypropyl, methacrylamido, chloropropyl,an alkyl chain (branched or linear) containing 1 to 12 carbon atoms, orepoxy, for example.

In one embodiment, the functional silane material comprises an epoxyfunctional group. In an alternative embodiment, the functional silanematerial comprises a hydroxyl or alkoxyl functional group.

In one embodiment, the functional silane material comprises at least twofunctional groups. The at least two functional groups may be differentfunctional groups. In such an embodiment, the functional silane materialmay comprise one or more epoxy functional group and one or more hydroxyor alkoxy functional group.

In one embodiment, the functional silane material comprises a silanematerial according to Formula I, or a polysiloxane polymer derived fromone or more silane material according to Formula I:(R¹)_(n)Si(OR²)_(m)  Iwherein each R¹ is independently selected from an epoxy functionaloptionally substituted alkyl group,each R² independently represents H or an alkyl groupn=1 to 3,m=1 to 3; andn+m=4.

Suitably, each R² may be independently selected from H, methyl, ethyl,propyl or butyl, particularly suitably H, methyl or ethyl.

Each optionally substituted alkyl group in R¹ may be independentlyselected from any optionally substituted C₁ to C₁₂ alkyl group.

In one embodiment, each R¹ is independently selected from an epoxy alkylor an epoxy alkyl ether.

The functional silane material may comprise γ-glycidyloxypropyltrialkoxy silane, such as γ-glycidyloxypropyl trimethoxy silane, forexample.

In one embodiment, the functional silane material may comprise one ormore amine functional groups and, optionally one or more hydroxy oralkoxy functional group.

In one embodiment, the functional silane material comprises a silanematerial according to Formula 2, or a polysiloxane polymer derived fromone or more silane material according to Formula 2:((R³)HN(CH₂)₃)_(n)Si(OR⁴)_(m)  2wherein each R³ is independently selected from H or an optionallysubstituted alkyl group,each R⁴ independently represents H or an alkyl groupn=1 to 3,m=1 to 3; andn+m=4.

Suitably, each R⁴ may be independently selected from H, methyl, ethyl,propyl or butyl, particularly suitably H, methyl or ethyl.

Each R³ may be independently selected from H or any optionally aminesubstituted C₁ to C₁₂ alkyl group.

In one embodiment, each R³ is independently selected from H or a primaryamine alkyl

The functional silane material may comprise an γ-amino propyl trialkoxysilane such as γ-amino propyl trimethoxy silane or anα-aminoethylaminopropyl trialkoxy silane, such asα-aminoethylaminopropyl trimethoxy silane(N-(3-(Trimethoxysilyl)propyl)ethylenediamine), for example.

The second component may further comprise at least one solvent, whichmay be an organic solvent.

Suitably, the coating composition when the two components are combinedto form one coating composition; comprises the acrylic latex materialand the functional silane material in a ratio of latex solids to silanesolids of between about 99:1 parts by wt to 1:99 parts by wt, especiallyin a ratio of between about to 60:40 parts by wt to 95:5 parts by wt andmore suitably in a ratio of between about 75:25 parts by wt to 90:10parts by wt. In one embodiment, the coating composition comprises theacrylic latex material and the functional silane material in a ratio oflatex solids to silane solids of between about 78:22 parts by wt to85:15 parts by wt.

In a preferred embodiment of the current invention the two componentcoating is applied as a repair coating for component parts of food andbeverage cans. A particularly preferred use is as a repair coating for afull aperture easy open end for food cans. This end component is repaircoated, after fabrication, by airless spraying of the material on to theexterior of the score line. Other uses as repair coatings include thecoating of seams and welds, such as side seams for which the coating maybe applied to the area by spraying (airless or air driven) or rollercoating. Repair coating can also include protection of vulnerable areaswhere corrosion may be likely due to damage, these areas includeflanges, rims and bottom rims where the coating may be applied byspraying, roller coating flow or dip coating.

In certain embodiments, the coating compositions of the presentinvention, may be substantially free, may be essentially free and/or maybe completely free of bisphenol A and derivatives or residues thereof,including bisphenol A (“BPA”) and bisphenol A diglycidyl ether(“BADGE”). Such coating compositions are sometimes referred to as “BPAnon intent” because BPA, including derivatives or residues thereof, arenot intentionally added but may be present in trace amounts because ofimpurities or unavoidable contamination from the environment. Thecoating compositions can also be substantially free and may beessentially free and/or may be completely free of bisphenol F andderivatives or residues thereof, including bisphenol F and bisphenol Fdiglycidyl ether (“BFDGE”). The term “substantially free” as used inthis context means the coating compositions contain less than 1000 partsper million (ppm), “essentially free” means less than 100 ppm and“completely free” means less than 20 parts per billion (ppb) of any ofthe above mentioned compounds, derivatives or residues thereof.

According to a second aspect of the present invention there is provideda food or beverage can comprising a surface having a coating on at leasta portion thereof, the coating being formed from a two component coatingcomposition according to the first aspect

According to a third aspect of the present invention there is provided amethod of repairing a food or beverage can, the method comprisingcoating a portion of the food or beverage can with a two componentcoating composition according to the first aspect.

It has been surprisingly and advantageously found by the presentinventors that the two component coating composition of the presentinvention provides a very clear coating with no perceptible yellowing ofthe coating. This is extremely advantageous in that the coatingcomposition, which is often used to repair a score line, issubstantially not visible to an end user. Therefore, according to afurther aspect of the present invention there is provided the use of twocomponent coating composition according to the first aspect for reducingyellowing.

It has also surprisingly and advantageously been found by the presentinventors that the addition of a functional silane material maysignificantly reduce the curing time of the coating composition.Therefore, according to a yet further aspect of the present inventionthere is provided the use of a functional silane in a second componentof a two component coating composition for reducing curing time of thecoating.

Preferably, the first component in the two component coating materialcomprises an acrylic latex material.

A yet further surprising element of the present invention is the thatthe addition of a functional silane material may significantly reducethe curing temperature of the coating composition. Therefore, accordingto a yet further aspect of the present invention there is provided theuse of a functional silane in a second component of a two componentcoating composition for reducing the curing temperature of the coating.Preferably, the first component of the two component coating compositioncomprises an acrylic latex material.

All of the features contained herein may be combined with any of theabove aspects and in any combination.

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example, to the following experimental data.

EXAMPLES

The following examples are intended to illustrate the invention andshould not be construed as limiting the invention in any way.

Polymer Examples

Core/shell latex emulsions were formed as follows.

Shell Polymer Example 1

The ingredients of this shell polymer example are displayed in Table 1below.

TABLE 1 Item no Component Parts (by weight) 1 Propylene glycol monomethyl ether 6.00 2 Butyl glycol 11.88 3 Trigonox 42S* 0.50 4 Butylglycol 3.00 5 Methacrylic acid 11.25 6 Ethyl acrylate 6.25 7 Styrene7.50 8 Butyl glycol 1.00 9 Trigonox 42S* 0.25 10 Butyl glycol 1.50 11Butyl glycol 0.50 12 De-ionized water 5.83 13 Dimethylethanolamine**5.83 14 De-ionized water 38.73 *= tert-Butylperoxy-3,5,5-trimethylhexanoate **= the amine used to neutralise thepolymerProcess Method

The polymerisation was carried out using a reaction vessel equipped withheating, cooling, stirring and a reflux condenser. A sparge of nitrogenwas applied to the reactor to provide an inert atmosphere, stirredvessels for mixing and addition of monomers (a monomer tank) and freeradical initiators (an initiator tank) were available and linked to thereaction vessel by pumps which could be used to control the additionrate. Items 1 and 2 were added to the reaction vessel and heated to 140°C. Whilst the vessel was heating to temperature items 3 and 4 were mixedin the initiator tank and items 5, 6 and 7 were mixed in the monomertank. With the contents of the reactor maintained at a temperature of139 to 140° C. the contents of the initiator tank and monomer tank weresimultaneously added to the reactor at a constant rate over a period of150 minutes. After the addition was completed the contents of thereactor were held at 139 to 140° C., then item 8 was added to thereactor from the monomer tank as a line wash. Items 9 and 10 were addedto the initiator tank. After holding the reactor contents at 139-140° C.for 30 minutes 50% of the contents of the initiator tank (items 9 and10) were added as rapidly as possible to the reactor and the temperatureof the reactor held at 139 to 140° C. for a further 30 minutes. Theremaining contents of the initiator tank were then added and item 11added to the reactor via the initiator tank as a line wash. The contentsof the reactor were then maintained at 139 to 140° C. for a further 90minutes. The reactor contents were then cooled to 98° C., items 12 and13 were mixed and the mixture was carefully added to the reactor over aperiod of 15 minutes. After thorough mixing of the contents of thereactor item 14 was added to produce a translucent or slightly hazysolution like material which was cooled to 25° C. and filtered ready foruse in further polymerisation.

The polymer obtained by the above example had the followingcharacteristics:

solids content 28.9% (180° C., 30 minutes 0.5 gm) viscosity 504centipoise (Brookfield DVII pro viscometer spindle 3, 50 rpm @ 25° C.)acid value 69.6 (mgKOH/gm on total sample)

This Shell polymer, also sometimes referred to as soap, can be used invarious core/shell latex systems. One example is detailed in table 2.

Latex Example 1

TABLE 2 Item Component Parts (by weight) 1 Shell polymer example 1¹25.38 2 De-ionized water 55.02 3 Styrene 6.80 4 Ethyl acrylate 9.54 5Glycidyl methacrylate 1.32 6 Trigonox 21² 0.18 7 De-ionized water 1.68 8Trigonox 21² 0.04 9 Trigonox 21² 0.04 ¹= the soap formed from thereaction components in Table 1, above ²= the radical initiator =tert-Butyl peroxy-2-ethylhexanoateProcess Method

Items 1 and 2 were placed in a reaction vessel equipped with heating,cooling, stirring and a simple reflux condenser. The vessel was alsosupplied with a nitrogen sparge to maintain an inert atmosphere and alsoattached were stirred addition tanks which could be employed to add αβunsaturated monomers and initiator. The mixture in the reaction vesselwas heated to 85° C. and held at that temperature. Items 3 to 6 weremixed in a stirred addition tank and then added to the vessel over aperiod of 2 hours, whilst maintaining the temperature of the contents ofthe vessel at 85° C. After the addition was complete item 7 was added tothe vessel via the stirrer addition tank as a line wash. The vessel wasmaintained at 85° C. for 30 minutes and then item 8 was added. Thevessel was maintained at temperature for a further 1 hour before item 9was added and the vessel was then maintained at 85° C. for a further 2hours. Finally the contents of the vessel were cooled to 40 C anddischarged with filtration prior to the use of this material, Latexexample 1, in the preparation of coatings.

The characteristics of the Latex produced in Latex example 1 weredetermined as follows:

Solids content 25.4% (110° C., 60 minutes 0.5 gm) Viscosity 15 seconds(Ford 4 cup @25° C.) Particle size 167.4 nanometers (Z average value,determined with diluted sample using Malvern Zetasizer Nano ZS machine)

The latex produced in this process is an example of a core shell latexdispersion, with a ratio of core to shell components of 73.3/26.7 wt %.

Coatings Examples Preparation of Coatings

Coatings were prepared from the Latex polymers as described below. Thecoatings were prepared as two parts, Part A and Part B, which are storedseparately as stable components. The two parts are then mixed in weightratios as outlined below prior to application of the coating.

The tables below outline the components of each of the parts and alsothe mixture of the parts which make up the coating. All the quantitiesgiven in the tables are parts by weight.

TABLE 3A Coating Coating Coating Components Example 1A Example 2AExample 3A Part A Latex Example 1¹ 85.92 82.29 0.00 Alberdingk AC 0.000.00 51.88 5503² Deionized Water 13.36 16.83 47.08 BYK-307³ 0.41 0.500.65 Optical Brightener⁴ 0.10 0.12 0.13 BYK-024⁵ 0.21 0.25 0.26 ¹= Coreshell Latex from preparative example 1 ²= Epoxy functional aqueousacrylic latex dispersion, commercially available from Alberdingk BoleyGMBH, Krefeld Germany ³= silicone wetting agent, commercially availablefrom BYK-Chemie GmbH, Wesel, Germany ⁴= Tinopal NFW Liq commerciallyavailable from BASF SE, Ludwigshafen, Germany ⁵= silicone defoamer,commercially available from BYK-Chemie GmbH, Wesel, Germany

Table 3A outlines the components of a composition which makes up part Awhich is the latex containing part of the two part coating. Each of theexamples was made by adding the components in order, as in the table, toa vessel stirred with a high speed mixer at 25° C. Mixing was continuedfor 10 minutes after the addition of components was complete.

TABLE 3B Coating Coating Coating Components Example 1B Example 2BExample 3B Part B Epoxy-methoxy 100.00 20.00 0.00 silane⁶ Amino-ethoxy0.00 0.00 21.55 silane⁷ Methoxypropanol 0.00 55.00 78.45 Acetone 0.0025.00 0.00 ⁶= Silquest A-187 commercially available from MomentivePerformance Materials Albany, NY, USA ⁷= Silquest A-1100 commerciallyavailable from Momentive Performance Materials Albany, NY, USA

Table 3B outlines the components of a composition which makes up part Bwhich is the functional silane containing part of the two part coating.Each of the examples was made by adding the components in order, as inthe table, to a vessel stirred with a high speed mixer at 25° C. Mixingwas continued for 10 minutes after the addition of components wascomplete.

TABLE 3C Coating Coating Coating Components Example 1 Example 2 Example3 Coating Coating Example 1A 97 Mixture Coating Example 2A 80 CoatingExample 3A 77 Coating Example 1B 3 Coating Example 2B 20 Coating Example3B 23

Table 3C outlines the component parts and the amounts which are mixed toproduce the final coatings. Thus Coating example 1 was prepared bymixing Coating example 1 A (part A or the latex part) with Coatingexample 1B (part B or the functional silane containing part) in theweight proportions as given in the table. Other examples were preparedby combining part A and part B as outlined in table 3C.

Each of the Coating examples were made by adding component B tocomponent A in a mixing vessel which was stirred with a high speedmixing blade at 500-1000 rpm at a temperature around 25° C. Mixingcontinued for 10 minutes after the addition was complete. After mixingeach of the coatings was ready for use; stored at a temperature around25° C. they remained in a useable state for around 50 hours.

Using the solids contents as determined for the latex materialsdiscussed above, the proportion of latex solids and silane solids ineach of the example coatings was calculated:

For coating example 1, the proportion of latex solids to silane solidsby weight is 87.6 to 12.4. For coating example 2, the proportions oflatex to silane solids by weight are 80.7 to 19.3 and for coatingexample 3, the latex to silane solids ratio is 80.3 to 19.7.

Coating Application and Drying

The Coatings from the coating examples outlined above and a commercialstandard product were applied to a metal substrate, being a fullaperture tinplate easy open end, such as those routinely used in food orbeverage cans. The ends used were coated with clear, gold or whitepigmented lacquer with print markings and had not been repair coated.

The coatings were applied with an airless spray gun in a strip 5-25 mmwide over the score line on the easy open end.

After application of the coatings the easy open ends were dried for oneminute in a fan assisted oven at a temperature between 100° C. and 150°C. as outlined in tables 4 and 5 below. The drying process produces acured film of the coating on the end which is tested, as outlined in thedetails below, to demonstrate the performance of the protective coatingapplied to the score line as a repair layer.

Details of Methods for Testing Coatings

The performance of the coatings are evaluated in the following ways:

The coating is evaluated using a test for bubbles, blush, adhesion andyellowing. Details of how these tests are performed and evaluated aregiven below.

Bubbles

After application and curing the formation of bubbles is evaluated. Thisis done by examining the score line with a microscope lookingparticularly for bubbles and defects which are trapped within the filmor in the coating metal interface. The evaluation is rated between 0 and5. Rating grade 0 corresponds to no bubbles seen along the score lineand grade 5 corresponds to bubbles covering all of the score line.

Blush

Blush is white colouration of the film caused by water penetration andentrapment. To assess the resistance to blush the coated ends aresterilised in an autoclave for 1 hour at 130° C. in water and in waterplus 1% teepol (sodium dodecyl benzene sulphonate, detergent) (asdetergent) and the film is observed.

In the evaluation of the coating examples reported below the blushevaluation corresponds to sterilisation in the liquid phase (completelyimmersed in the solution) in water with 1% arylsulphosuccinate detergentfor 1 hour at 130° C.

After sterilisation the appearance of the film is rated between 0 and 5.Grade 0 corresponds to perfect film appearance with no discernableattack. Grade 5 corresponds to complete attack of the film across thewhole of the score line.

The industrial process for processing or sterilisation of canscontaining various food stuffs often uses water which is treated withdetergents such as arylsulphosuccinates. In some cases the industrialprocess can also use a 1% solution of Teepol in water. Hence, this testhas particular relevance to the industrial use of the coatings that areunder evaluation.

Adhesion

Film adhesion after sterilisation with water with 1% teepol (sodiumdodecyl benzene sulphonate, detergent) for 1 hour at 130° C. is alsochecked. The coating is crosshatched and checked for removal with tape(3M 610 type tape). Grade 0 corresponds to good adhesion with no removalof coating and grade 5 to complete loss of adhesion as seen by completeremoval of the coating with the tape.

Yellowing

To check yellowing the coating is applied on ends which are coated withwhite enamel and sterilized in water with 1% teepol (sodium dodecylbenzene sulphonate, detergent) for 1 hour at 130° C. Grade 0 correspondsto no yellowing and grade 5 to a high yellowing level.

Results of Testing of Coating Examples

The standard product and coating examples were prepared, applied anddried as outlined in the preceding descriptions. The coated endsobtained were then tested no later than 3 hours after completion of thedrying process. The results of the testing and evaluation of the endsare compiled in Table 4. It should also be noted that for each coatingends were cured at three different temperatures (105° C., 120° C. and150° C.) as outlined in the table.

TABLE 4 Adhesion Film curing after temperature Bubbles Blushsterilisation Yellowing Standard from 105° C. 0 4 0 1 PPG (epoxy 120° C.0 3 0 1 based solvent- 150° C. 0 2 0 1 borne product)¹ Coating 105° C. 02 0 0 Example 1 120° C. 0 2 0 0 150° C. 0 2 0 0 Coating 105° C. 0 1 0 0Example 2 120° C. 0 1 0 0 150° C. 0 1 0 0 Coating 105° C. 0 1 0 0Example 3 120° C. 0 1 0 0 150° C. 0 1 0 0 ¹= PPG 2982-803/A + PPG2982-804/A mix 1:1

The results in table 4 show that the standard product has poor blushperformance particularly where the curing temperature used is low (105°C. and 120° C.). This is expected for the standard; in commercialproduction using products such as the standard employed here, therepaired easy open ends are held at a temperature around 22° C. for aperiod at least 24 hours to fully develop resistance properties. All ofthe coating examples under study at all of the temperatures show abetter level of performance than the standard and have been shown todevelop a good level of performance immediately after oven drying, withno need to age the coating. This offers an advantage, particularly inprocess costs, for the products under study compared to the standard.

Tables 5 below shows the results of tests on ends which have been storedat a temperature of 19 and 22° C. for 24 hours after oven drying. Thisstorage or ageing process is applied in commercial use of the standardcoating which is known not to develop its full performance immediatelyafter drying. Tests were made for the standard and the coating examplesunder study after this storage time and the results should be comparedto those in table 4

TABLE 5 Adhesion Film curing after temperature Bubbles Blushsterilisation Yellowing Standard from 105° C. 0 2 0 1 PPG (epoxy 120° C.0 1 0 1 based solvent- 150° C. 0 1 0 1 borne product)¹ Coating 105° C. 02 0 0 Example 1 120° C. 0 2 0 0 150° C. 0 2 0 0 Coating 105° C. 0 1 0 0Example 2 120° C. 0 1 0 0 150° C. 0 1 0 0 Coating 105° C. 0 1 0 0Example 3 120° C. 0 1 0 0 150° C. 0 1 0 0 ¹= PPG 2982-803/A + PPG2982-804/A mix 1:1

The results in table 5 when compared to those in table 4 show that theperformance of the standard has changed and reached a good level ofperformance. This change was as expected for the commercial standardproduct. Whereas for all the coating examples under study the testresults in table 4, immediately after cure, are the same as the resultsin table 5, after 24 hours ageing. The results in table 5 of all thecoating examples under test are comparable with the standard.

In all of the examples under study the film is transparent and iscolourless, as indicated by a score of 0 in the yellowing test, whereasthe standard is known to be slightly yellowish, as indicated by a scoreof 1 in the yellowing test, giving the repair some visibility. Hence,the coatings under study offer another desirable advantage over thecurrent commercial standard product, particularly where the ends areprecoated with a pigmented white coating or colourless lacquer.

Thus in summary, it can be seen from the examples above that a coatingcomposition made in accordance with the present invention provides awater based coating with lower volatile organic content (VOC), requiresa lower curing temperature, does not need to be stored (or aged) toproduce the desired protection performance and produces less yellowingcompared to the current commercial standard product. Furthermore, it canbe seen from the examples presented that in common with the currentcommercial standard product the coating composition made in accordancewith the present invention provides a two component coating with aworkable life (after mixing of the components) of at least 12 hours, canbe applied with airless spray equipment and provides sufficientprotection to resist corrosion to the exposed metal score line which ithas been applied to repair.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A two component coating compositionsuitable for coating onto a metal substrate, the coating compositioncomprising: a first component comprising an acrylic latex material; anda second component comprising a functional silane material; wherein theacrylic latex material comprises an alkyl (meth)acrylate which comprisesepoxy functionality.
 2. The coating composition of claim 1, wherein theacrylic latex material comprises an aqueous emulsion of one or moreacrylic polymers.
 3. The coating composition of claim 1, wherein theacrylic latex material comprises an aqueous dispersion of an acrylicmaterial in a core/shell arrangement.
 4. The coating composition ofclaim 3, wherein the core is formed from a core mixture and the shell isformed from a shell mixture, and wherein the ratio of the core mixture(monomers and initiator) to shell mixture (monomers and initiator) isbetween about 20:80 and 90:10 by weight.
 5. The coating composition ofclaim 1, wherein the latex material comprises an aqueous dispersion ofan acrylic material with reactive functional groups and stabilized withan emulsifier or surfactant material.
 6. The coating composition ofclaim 1, wherein the functional silane material comprises a silanematerial according to Formula I, or a polysiloxane polymer derived fromone or more silane material according to Formula I:(R¹)_(n)Si(OR²)_(m)  I wherein each R¹ is independently selected from anepoxy functional optionally substituted alkyl group, each R²independently represents H or an alkyl group n=1 to 3, m=1 to 3; andn+m=4.
 7. The coating composition of claim 1, wherein the functionalsilane material comprises a silane material according to Formula 2, or apolysiloxane polymer derived from one or more silane material accordingto Formula 2:((R³)HN(CH₂)₃)_(n)Si(OR⁴)_(m)  2 wherein each R³ is independentlyselected from H or an optionally substituted alkyl group, each R⁴independently represents H or an alkyl group n=1 to 3, m=1 to 3; andn+m=4.
 8. The coating composition of claim 1, wherein the functionalsilane material comprises an epoxy functional silane or an aminofunctional silane.
 9. The coating composition of claim 1, wherein thecoating composition comprises the acrylic latex material and thefunctional silane material in a ratio of latex solids to silane solidsof between about 99:1 parts by wt to 1:99 parts by wt.
 10. The coatingcomposition of claim 1, wherein the functional silane material reducesthe curing time in a two component coating composition as compared to acoating lacking the functional silane material.
 11. The coatingcomposition of claim 1, wherein the functional silane material reducesthe curing temperature in a two component coating composition ascompared to a coating lacking the functional silane material.
 12. Thecoating composition of claim 1, wherein the alkyl (meth)acrylatecomprises glycidyl methacrylate.
 13. The coating composition of claim 6,wherein the functional silane material comprises γ-glycidyloxypropyltrialkoxysilane.
 14. The coating composition of claim 7, wherein thefunctional silane material comprises γ-aminopropyl trialkoxysilane.